Pointing at people is considered impolite in some cultures. I think it's better to raise your hand with an extended finger and then cross both your index fingers to signal "close out."
Have a little light on the table with a button you can push to summon the server.
This is similar to how in Brazilian churrascarias you have a red/green coaster that you flip green if you want the server to come around with more meat, and red, when you're done.
The way my wife currently does it (she's Asian) is that she uses her index fingers and thumbs to "air draw" a rectangle which I guess is supposed to represent a cheque